1. Field of the Invention
The invention is directed to a telescoping drive shaft having internal passages for directing lubricating grease to the engaging assemblies of the shaft elements.
2. Description of the Prior Art
Many large four-wheel drive work vehicles, such as agricultural tractors, industrial loaders, and logging skidders are articulated in the middle. That is, the front and rear wheel assemblies can pivot with respect to one another. Typically, the front wheels are provided with a differential mounted on a front housing portion whereas the rear wheels are provided with a rear differential mounted on a rear housing portion. The two housing portions are pivotally coupled to one another along a vertical axis. To transmit power to each differential assembly, a drive line extends across the articulation point. To account for changes in length of the drive line as the vehicle articulates, a portion of the drive line includes a telescoping drive shaft. This drive shaft is provided with universal couplings at either end to account for axial misalignment.
As shown in FIG. 2A which illustrates a prior art telescoping drive shaft, the drive shaft comprises a first drive shaft element 10 telescopicingly receives second drive shaft element 12. The first drive shaft element is provided with internal splines 14 which cooperate with external splines 16 of the second shaft element forming engaging assemblies. In this way, rotational movement can be transmitted between the two drive shaft elements, and, therefore, across the drive line. It should be appreciated that the two drive shaft elements can reciprocate relative to one another.
To assure that the drive shaft elements can reciprocate relative to one another, it is necessary that the splines be adequately lubricated. To accomplish this, lubricating grease is injected through grease fitting 18 into the hollow interior formed by the first shaft element. The lubricating grease is held in this hollow interior which forms a lubricant holding chamber 20. As the drive shaft elements reciprocate with respect to one another, the lubricant is forced along the splines lubricating them. Excess lubricant is exhausted through aperture 24 formed in end plate 26. The assembly is also provided with a seal 28 located at the end of first drive shaft element 10.
Telescoping drive shafts such as the one discussed above have not proved to be entirely satisfactory. The majority of the fresh grease injected into chamber 20 is typically exhausted through aperture 24 and does not reach the intermeshed splines.